We present a study of MSX point sources in the Galactic bulge ( | l | < 3 ^ { \circ } , 1 ^ { \circ } < | b | < 5 ^ { \circ } ) , observed at A , C , D and E-band ( 8 to 21 \mu m ) , with a total area \sim 48 deg ^ { 2 } and more than 7000 detected sources in the MSX D-band ( 15 \mu m ) .
We discuss the nature of the MSX sources ( mostly AGB stars ) , their luminosities , the interstellar extinction , the mass-loss rate distribution and the total mass-loss rate in the bulge .
The mid-infrared data of MSX point sources have been combined with the near-infrared ( J , H and K _ { s } ) data of 2MASS survey .
The cross-identification was restricted to K _ { s } -band detected sources with K _ { s } \leq 11 mag .
However , for those bright MSX D-band sources ( [ D ] < 4.0 mag ) , which do not satisfy this criteria , we have set no K _ { s } -band magnitude cut off .
The bolometric magnitudes and the corresponding luminosities of the MSX sources were derived by fitting blackbody curves .
The relation between \dot { M } and ( K _ { s } - [ 15 ] ) _ { 0 } was used to derive the mass-loss rate of each MSX source in the bulge fields .
Except for very few post-AGB stars , planetary nebulae and OH/IR stars , a large fraction of the detected sources at 15 \mu m ( MSX D-band ) are AGB stars well above the RGB tip .
A number of them show an excess in ( [ A ] - [ D ] ) _ { 0 } and ( K _ { s } - [ D ] ) _ { 0 } colours , characteristic of mass-loss .
These colours , especially ( K _ { s } - [ D ] ) _ { 0 } , enable estimation of the mass-loss rates ( \dot { M } ) of the sources in the bulge fields which range from 10 ^ { -7 } to 10 ^ { -4 } M _ { \odot } yr ^ { -1 } .
Taking into consideration the completeness of the mass-loss rate bins , we find that the contribution to the integrated mass-loss is probably dominated by mass-loss rates larger than 3 \times 10 ^ { -7 } M _ { \odot } yr ^ { -1 } and is about 1.96 \times 10 ^ { -4 } M _ { \odot } yr ^ { -1 } deg ^ { -2 } in the “ intermediate ” and “ outer ” bulge fields of sources with mass-loss rates , \dot { M } > 3 \times 10 ^ { -7 } M _ { \odot } yr ^ { -1 } .
The corresponding integrated mass-loss rate per unit stellar mass is 0.48 \times 10 ^ { -11 } yr ^ { -1 } .
Apart from this , the various mid- and near-infrared colour-colour and colour-magnitude diagrams are discussed in the paper to study the nature of the stellar population in the MSX bulge fields .